Many companies, including those in the food and beverage, pharmaceutical, cosmetics, manufacturing and electronics industries, recognize the negative effects on quality created by oil contact with their product during production. Product rejections and consumer safety concerns associated with oil contamination can have broad negative financial and commercial impacts on a company. However, an often overlooked source of oil in compressed air — ambient air — is frequently misunderstood, underestimated or ignored.

In this blog, we’ll examine the effect that ambient oil vapour levels can have on downstream compressed air quality and what to consider when looking for technically oil-free compressed air to ISO8573-1 Class 0 or Class 1 for total oil.

What is ambient air?

Ambient air is the air we breathe and it’s all around us. It’s also the air that is drawn in by air compressors. Ambient air is made up of approximately 78% nitrogen and 21% oxygen. The remaining 1% contains a mix of argon, carbon, helium and hydrogen as well as a variety of contaminants — oil vapour being one of them. Ambient air is an often overlooked source of contamination that can have a big impact on a compressed air system.

How is ambient air contaminated?

Ambient air quality is directly impacted by air pollution caused by industrial processes such as burning fossil fuels and emissions from vehicle exhaust, oil and gas fields, paints, and solvents.

Oil vapour in ambient air is made up of a combination of hydrocarbons and volatile organic compounds (VOC). Ambient air typically contains between 0.05mg/m3 and 0.5mg/m3 of oil vapor, however, levels can be higher in dense, urban or industrial environments or next to car parks and busy roadways.

These levels may seem negligible, but when it comes to compressed air contamination, we must consider the effect that compressing the air has on the ambient contamination, the amount flowing into the compressed air system, and the time the compressor is operating.

Compressing air – compounding the problem?

The process of compression, as well as flow rate and time, build the level of oil in the compressed air that travels through a production system — air that eventually finds its way to production equipment, instrumentation, products and packaging materials.

Compression, or pressurizing the compressed air, can significantly increase the volume of oil. The greater the operating pressure, the higher the potential level of oil in the compressed air. This is compounded by the flow rate and time of operation. Compressors are often designed to operate continuously. This means that the concentration of oil continues to multiply in the confined space of the compressed air system. In turn, it will only exit the system at points where the air is released. These exit points are often in areas where the contaminated air comes in contact with product, production equipment or instrumentation. So, what may seem like negligible levels of hydrocarbons and VOC in ambient air, can become a great concern when the same is drawn in and compressed for use in manufacturing.

Effect on quality

Once inside the compressed air system, oil vapour will cool and condense, mixing with water in the air. This contamination causes numerous problems to the compressed air storage and distribution system, production equipment and final product leading to:

Inefficient production processes.

Spoiled, damaged or reworked products.

Reduced production efficiency.

Increased manufacturing costs.

Oil-free compressors

Due to the financial and commercial impact of contaminated product, many companies specify the use of an oil-free compressor, in the mistaken belief that this will deliver oil-free compressed air to critical applications.

Oil-free compressed air systems are typically installed without downstream purification equipment intended to remove oil, as they are deemed unnecessary accompaniments. While it is true that oil-free compressed air systems will not contribute contamination in the manner that oil lubricated systems will, oil vapour from ambient air remains untreated.

Considerations for technically oil-free air

Technically oil-free air, in accordance with ISO8573-1 (international standard for compressed air purity) Class 0 or Class 1 for Total Oil, can only be guaranteed through the proper application of downstream purification equipment. This equipment may include water separators and coalescing filters to remove liquid water and oil, aerosols of water and oil, and solid particulate as well as adsorption filters to treat oil vapour. Compressed air users seeking an oil-free source of air would be wise to consider these precautionary purification steps, whether they are used with oil-lubricated or oil-free compressed air systems.

In order to establish compliance with ISO8573-1 Class 0 or Class 1, the international standards categorizing oil level in compressed air, users must perform tests to assess both oil aerosol and oil vapor presence in their systems. The levels of each phase will combine to establish total oil in the compressed air system.

To conduct the tests, samples of each phase must be drawn through a solvent extraction process and analyzed using gas chromatography (GC) or Fourier transform infrared (FT-IR) technology. The combination of the two methods will provide an accurate reading down to 0.003mg/m3.

While there are other methods for testing oil levels, like Photo Ionisation Detector (PID), these will leave certain compounds undetected. To this end, they should be used for estimation purposes only. GC and FT-IR will provide results that can be related to ISO standards with reliable and complete accuracy.

Advanced solutions

Parker has recently introduced a new compressed air purification system. The OFAS Oil Free Air System is a fully integrated heatless compressed air dryer and filtration package suitable for use with any compressor type and can be installed in the compressor room or at the point of use. Fitted with a third adsorbent column for oil vapour removal, the OFAS has been third-party validated by Lloyds register to provide ISO 8573-1 Class 0, with respect to total oil from both oil-lubricated and oil free compressors, ensuring the highest quality air at the point of use for critical applications.

Conclusion

Compressed air is vital to any production process. Whether it comes into direct contact with the product or is used to automate a process, a clean, dry reliable compressed air supply is essential. If the compressed air contains oil, the consequences can be high both financially and in terms of brand damage.

In an industrial manufacturing plant, coalescing filters are
probably the most important piece of purification equipment found
in a compressed air system. They treat six of the ten main
contaminants...

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